Chapter 160: In the End, It Still Has to Be Faced

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It was only a matter of time before the capital sent people to the base. Director Bai had been overseeing revisions to the old military standards for several months. During that time, Yang Hui had familiarized himself with every aspect of the institute’s work, large and small, while the revision of the standards had begun to proceed along the right track. Director Bai had apparently worked out a method for revising them, and the development of engine components under the guidance of the new standards had already begun to show results.

“Yang Hui, you probably know that the capital has sent people to investigate why we have not been designing according to military-standard regulations. I hear that people from the higher authorities’ Office for the Revision of Aviation Industry Standards are coming, and that Senior Engineer Wu is coming as well. It feels like a storm is about to break. If something happens to me this time, you must carry on the banner and see this engine through to completion.”

A gloomy mood filled Director Bai’s office. Despite Director Bai’s repeated warnings, Yang Hui had not taken part in revising the new standards. At present, he had no particularly good solution to the problems posed by those standards—but at this very moment, he had thought of a way to deal with the investigation team from above.

“Director, the core engine for our new engine seems to be progressing very well. When do you think we can begin test runs? That is extremely important to us right now.”

At the mention of the core engine, Director Bai had no reason not to be excited. The development of the new engine’s core was going remarkably well. The compressor had not been altered, but the combustor and high-temperature turbine had undergone major redesigns, and progress had nevertheless been excellent.

Speaking of the core-engine project, Director Bai temporarily forgot his earlier worries and began describing the latest developments.

“For the new engine, we have introduced the concept of a core engine. Although all the engine’s subsystems are being developed in parallel, the core engine itself is being developed as an integrated whole.”

The core engine consisted of the high-pressure compressor, combustor, and high-temperature turbine, together with a main shaft connecting the high-pressure compressor and high-pressure turbine. These three components were the most critical parts of an aircraft engine, and also the parts most prone to failure. To solve the problems associated with them, engineers had developed the concept of integrating the core engine and designing it as a single large system.

Director Bai continued by outlining the progress on the core engine’s major components.

“We made no changes to the high-pressure compressor. Once we obtained its technical data, we began testing it. Using damage-tolerance design theory, we discovered some very pleasant surprises during the tests.”

The more he spoke, the more excited he became. Director Bai rose from his chair, found the high-pressure compressor’s test data amid the piles of documents, and confidently pushed it across the desk toward Yang Hui.

“Take a look. This is the test data for our high-pressure compressor. It was the first component to complete testing, and the results are extremely encouraging.”

Yang Hui picked up the documents and studied them carefully. The data were indeed just as Director Bai had said. He was so excited that his hands trembled around the papers. This was truly beyond his expectations.

“The first fatigue cracks appeared after eleven hundred hours. Following prolonged testing, the compressor blades fractured at seventeen hundred hours, and extensive damage began at eighteen hundred hours. This is excellent news. If the compressor can really last that long, we will have nothing to worry about on that front. Even if we calculate conservatively, we should still be able to achieve a service life of fourteen hundred hours.”

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That was the nature of damage-tolerance design. Components usually had a long period of usable life between the appearance of cracks and their final failure, but a margin had to be reserved during the design process.

Take the high-pressure compressor, for example. Its first fracture occurred at seventeen hundred hours. If its economical service life was conservatively set at fourteen hundred hours, the remaining three hundred hours would serve as a margin of safety. With such a margin, the risk could be kept to a minimum.

After hearing Yang Hui speak from the heart in his excitement, Director Bai nodded emphatically.

“Yes. Designed according to the principles of damage tolerance, our high-pressure compressor can have its service life extended to fourteen hundred hours.”

After finishing with the compressor data, Director Bai took out another document pouch. The pouch bore the seal of Hongqi Factory. Yang Hui did not know what was inside, but it was clear that the contents were related to Hongqi Factory.

The bulging pouch was filled with technical documents—the data Hongqi Factory had just submitted.

“Take a look at this. These are the test results for the main shaft of the new engine’s high-pressure rotor, which we commissioned Hongqi Factory to develop. They conducted the tests according to our requirements and in line with damage-tolerance design principles. The main shaft has performed just as well. One surprise after another.”

Yang Hui did not wait for Director Bai to prolong the suspense. He took the documents directly from his hands. Hongqi Factory had considerable expertise in researching engine service life.

There was no need to mention the turbofan engine they would struggle for years to develop in later generations, suffering repeated setbacks before finally succeeding. That engine was already famous for its long service life, and its technology had come from Britain, so it could not truly demonstrate Hongqi Factory’s own capabilities. The factory’s real strength was reflected in its principal product, the WP-8 turbojet—the engine that powered the Republic’s H-6 bomber.

Since the WP-8 entered military service in 1967, years of improvements had brought its first overhaul interval to eight hundred hours by 1983. That was no ordinary achievement. The total service life of its Soviet prototype, the AM-3 engine, was only eight hundred hours as well.

Yet the two figures meant entirely different things. During eight hundred hours of service, the WP-8 required little cause for concern beyond routine maintenance. After eight hundred hours, it could undergo a major overhaul and continue operating; surpassing a thousand hours of total service life was effortless. The AM-3 prototype, by contrast, was scrapped outright after eight hundred hours.

All of this reflected Hongqi Factory’s mastery of engine longevity. Naturally, the results were different when the new engine’s main shaft was entrusted to them.

The data stated: “The first cracks in this batch of high-pressure compressor main shafts appeared at fourteen hundred hours, while fractures occurred at sixteen hundred hours. This is an excellent result. We should be able to set the main shaft’s service life at exactly fourteen hundred hours without any problem.”

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Although engine main shafts were subject to extremely demanding requirements and could not develop cracks during operation, this was not an absolute rule. Under the principles of damage-tolerance design, setting the service life to coincide with the period when cracks first appeared was perfectly acceptable.

Fourteen hundred hours was exactly when the first cracks appeared. Director Bai was more cautious about this matter. The main shaft was the last component on which they could afford to be careless, so he set its total service life at thirteen hundred and fifty hours.

“That’s right. An engine main shaft has no concept of a first overhaul. The moment a crack appears, it must be scrapped. After thinking it over carefully, I decided not to use damage-tolerance design for this most important load-bearing component. We will design it according to fatigue life instead. Thirteen hundred and fifty hours will be the absolute upper limit of its service life. A margin of fifty hours should be sufficient.”

Yang Hui largely supported Director Bai’s decision. There could be no room for the slightest risk where the main shaft was concerned. Besides, thirteen hundred and fifty hours was still an excellent result—only fifty hours less than the compressor’s economical service life, which was entirely acceptable.

“There’s nothing wrong with being conservative. Setting the service lives of these two most important components at thirteen hundred and fifty hours will more or less determine the total service life of the engine. Thirteen hundred and fifty hours is vastly better than the service life of our WP-7—nearly twice as long, in fact.”

The combustor and high-temperature turbine were still undergoing testing, so their precise service lives were not yet known. Even so, Director Bai had great confidence in both components.

“Our combustor and high-temperature turbine are now being tested. We do not yet know their exact service lives, but the first cracks in the combustor were expected at four hundred hours. It has now reached five hundred hours without any problems. According to our calculations, the combustor should require its first overhaul at around six hundred hours. That means the first overhaul of our new engine should also be scheduled for then.”

The combustor was a high-temperature component and the part most likely to develop problems. Service life had always been the weak point of aircraft engines—the shortest stave in the barrel.

“Yes, Director. Time really flies. The combustor and high-temperature turbine have already been produced. That is somewhat beyond expectations.”

Yang Hui sighed with emotion, and Director Bai did the same.

“Yes. We are already approaching a full year. We secured this project last July, and now it is March—eight whole months. It has not been easy secretly revising the design specifications while concealing what we were doing for four and a half months.”

To be continued.